The prospect of the United States Congress sabotaging an international nuclear agreement with Iran, moving us closer to a military crisis, is no longer an abstraction. Legislation to impose new sanctions, which would derail historic diplomatic progress, now has bipartisan majority support in the House and Senate, and the White House is making no secret of its concern.

If you’re not taking the debate seriously, it’s time to start.

Jeffrey Goldberg, a self-described “hawk” when it comes to U.S. policy towards Iran, made a persuasive case yesterday that Congress is making a terrible mistake.

What it could do is move the U.S. closer to war with Iran and, crucially, make Iran appear – even to many of the U.S.’s allies – to be the victim of American intransigence, even aggression. It would be quite an achievement to allow Iran, the world’s foremost state sponsor of terrorism, to play the role of injured party in this drama. But the Senate is poised to do just that.

Goldberg added “negotiations remain the best way to stop Iran from crossing the nuclear threshold.” If Congress deliberately forces the talks to collapse, a military strike becomes more likely, which raises the prospect of another national security crisis, and which would strengthen the very Iranian hardliners the U.S. hopes to weaken. At the same time, it would signal to the world that Americans are not to be trusted when we say we’re committed to peaceful solutions, causing lasting damage to our ability to garner international support.

For his part, House Majority Leader Eric Cantor (R-Va.) argued yesterday, “I believe strongly that we ought to have in place sanctions that will occur when the Iranians inevitably break their word. We can’t trust the Iranians.”

What Cantor continues to struggle with are the basics of the debate – if Iranians break their word, Congress can pass additional sanctions. Why undermine diplomatic efforts and the United States’ credibility on the global stage, on purpose, in anticipation of a breakdown that hasn’t happened? What possible reason could there be to rush us closer to a crisis when the talks are still progressing?

As the political dispute on Capitol Hill intensifies, getting a reliable head count of how many senators there are in the pro-sabotage camp becomes all the more important – and yesterday was an eventful day.

As of Monday, 58 senators – including 16 Democrats – had endorsed a bill for new sanctions, though roughly 30 Senate Democrats had not yet taken a position. If the bill has 60 supporters, it can withstand a filibuster; if it gets to 67 votes, proponents can override President Obama’s promised veto.

So what happened yesterday? Quite a bit:

* Sen. Tim Kaine (D-Va.) announced his opposition to the bill. So did Sens. Jeff Merkley (D-Ore.) and Chris Murphy (D-Conn.).

* Sens. Jeff Flake (R-Ariz.) and Rand Paul (R-Ky.) are rare undecided votes within the GOP camp, though Flake says he “thinks” the sanctions bill would be a “net plus.” He didn’t say for whom.

* Sen. Al Franken (D-Minn.) hasn’t taken a firm position, but appears to be leaning “no.”

* Sen. Richard Blumenthal (D-Conn.) was a “yes” vote, but seemed to hedge a bit yesterday. “Well I think the Iran sanctions bill is meant to strengthen the president, not in any way impede the ongoing negotiations, which should and hopefully will be successful,” Blumenthal told reporters. “So as long as there’s progress, and as long as the progress is meaningful and visible, there may not need to be a vote.”

As for Senate Majority Leader Harry Reid (D-Nev.), who opposes the sanctions bill, he’s not sure what to do next.

Senate Majority Leader Harry Reid is showing no signs of bringing the Iran sanctions bill closer to a vote as Democrats in the Senate continue to stay mum on the issue.

“The one message that the Iranians should have if they don’t have it by now is that we are not going to allow them to have nuclear weapons,” Reid told reporters on Tuesday. “While this process is playing out, that as the negotiations are going on in Switzerland or wherever they’re going on – I don’t know, they keep changing the place – while they’re going on and while the legislative process is working forward here, I’m going to sit and be as fair an umpire as I can be.”

“I think at this stage, I think we’re where we should be,” Reid said. “There’s 10 senators who, chairmen of committees here, have said they don’t want anything done. We have now, I don’t know how many senators, but more than 55 are co-sponsoring this. So this – we’re going to wait and see how this plays out.”

President Obama is scheduled to meet with the entire Senate Democratic caucus at the White House today. Iran will be a major topic of conversation.